Goal-directed perceptual decisions involve separable neurobiological mechanisms that sort incoming sensory information, accumulate goal-relevant data, compare accumulated data with a boundary, and commit to response upon reaching a decision. Disruption of any of these stages can impair the effectiveness of daily decisions, which may have serious consequences for health and well-being by affecting basic skills such as driving, social interaction, reading, and memory. While there have been significant advances in understanding the neural basis of these processes, the mechanisms by which sensory evidence is gathered, maintained, and evaluated are poorly understood. The proposed research will use functional magnetic resonance imaging (fMRI) to study the topography and temporal signature of neural systems involved in perceptual decision making and identify how they relate to choice outcome. Our previous research on object identification indicates that signals related to sensory processing, evidence gathering, and the commitment to a decision are temporally dissociable using fMRI. The first aim of the proposed work is to establish a link between research using single unit physiology in non-human primates and research using functional imaging in humans, and to examine the relationship between sources of evidence and fMRI measures of evidence accumulation. The second aim is to test the hypothesis that the magnitude of fMRI activity in accumulator areas is related to choice criterion. Establishing this relationship will inform neurocognitive models of decision making and may identify effective compensatory strategies and appropriate target domains for remediation of faulty decision making. The third aim will examine the relationship between neural signals and perceptual abilities in healthy aging. The proposed research will permit the development of a framework relating basic principles derived from neurophysiological research to measures of neural functioning in humans, and will inform theoretical models of perceptual decisions. The experiments will also serve as a basis for future research on more complex decisions, such as those involving reasoning, and for research aimed at early detection of disease states associated with faulty decision processing, such as Alzheimer's disease.